There are many processes for manufacturing polyolefins such as polyethylene, polypropylene, ethylene propylene rubber. Catalysts or initiators convert olefins, and optionally comonomers, into polyolefins. Development of new, better performing, less costly polyolefins has often been a result of catalyst development.
Polyolefin catalysts, such as Ziegler-Natta catalysts systems, are transition metal compounds like transition metal halides or transition metal alkoxy halides. These transition metal compounds are co-catalyzed with aluminum alkyls to form a catalyst system. It is estimated that close to 9,000 tons of Ziegler-Natta type catalysts were manufactured in 1992 to meet the worldwide capacity demand for polyolefins.
Metallocene compounds co-catalyzed with alumoxane compounds form the basis for another polyolefin catalyst system based on transition metal compounds and aluminum compounds. Examples of the latter are U.S. Pat. No. 4,937,299 and EPA 0-129368 to Ewen, et al. and U.S. Pat. No. 4,808,561 to Welborn, Jr.
Catalysts tend to be active chemical compounds and those most often used for polyolefin formation are based on one or more transition metals. Many such catalysts are pyrophoric, igniting on contact with air and/or moisture. The active chemical characteristics of these catalysts make them desirable and useful as polymerization catalysts.
Deactivation and subsequent disposal of active catalysts is a problem. This problem is caused by catalyst manufacture that results in catalysts that do not meet the manufacturer's specifications, or even meeting those specifications, they may not meet the performance specifications of the catalyst user. Also, after polymerization, "heels" of active catalyst remain after polymer discharge from a reaction vessel. These "heels" are catalysts that are still active. Additionally, under normal manufacturing techniques, more catalysts will be produced than used. All of these situations result in active catalysts that must be disposed of safely.
Catalyst deactivation techniques are known. For example, flooding with water, alcohol, or similar liquid treatments cause the active chemicals of the catalyst to react violently with the flooding medium and/or themselves, resulting in inert or relatively inert substances. The flooding medium may be removed from the now inert or relatively inert catalyst components or alternatively the flooding medium and the deactivated catalyst are kept together for disposal.
Often after such flooding, the catalyst is no longer pyrophoric, and therefore relatively safe for disposal.
However, the flooding medium after catalyst contact, contains components that result from contact with and reaction with the catalyst. The flooding medium, after catalyst contact, may have a flash point that is lowered by volatile organic chemicals and a pH that is slightly to highly acidic.
A waste stream with a low flash point and low pH, will likely be categorized as hazardous. Such hazardous categorization will result in increased disposal costs. Such costs are escalating as environmental laws become more stringent.
In addition to flooding, other catalyst deactivation techniques, such as by exposure to air/oxygen, may be used. This technique, like flooding, causes the active chemicals of the catalyst to react violently, resulting in inert or relatively inert substances. This method, because of the violent reaction, is useful only for very small amounts of catalyst. This method may be preferably used for small amounts of catalyst, such as might be remaining on vessel walls after removal of a batch of catalyst.
It would be desirable to have a process that would allow catalyst deactivation at lower cost and fewer potential environmental concerns than previous deactivation methods.